The present invention relates to improvements in the torque characteristics and the heat generation characteristics of a radial roller bearing, such as a tapered roller bearing.
Usually, a tapered roller bearing comprises an inner ring having a cone back face rib, an outer ring mounted opposite to the inner ring, and tapered rollers disposed between the inner and outer rings. When the tapered roller bearing is used, the rolling contact surfaces of the tapered rollers make contact with the raceway surfaces of the inner and outer rings. Also, a larger end face of each tapered roller makes contact with the surface of the cone back face rib of the inner ring. If the degree to which these portions make contact with each other is not maintained appropriately, then the running torque increases as a result of high frictional resistance. Also, the amount of heat frictionally produced initially increases.
The aforementioned degree to which the rolling contact surfaces of the tapered rollers make contact with the raceway surfaces of the inner and outer rings can be adjusted by crowning the rolling contact surfaces of the tapered roller or the raceway surface of the inner or outer ring that makes contact with the rolling contact surfaces of the tapered rollers. The amount of crowning is given by .DELTA.t/l i.e., the ratio of the depth of crowning .DELTA.t to the effective roller length of l. As the amount .DELTA.t/l increases, a point contact is approximated, and the degree of contact reduced. Where the amount of .DELTA.t/l is small, a line contact is approximated, and the degree of contact increases. Accordingly, increasing the amount of crowning .DELTA.t/l would be contemplated to reduce frictional resistance. However, if the amount of crowning .DELTA.t/l becomes too large, then the tapered rollers are spaced a large distance from the inner and outer rings. This results in a thick film of oil, which in turn increases the viscous resistance.
In the past, the inner surface of the cone back face rib had been finished roughly and so this surface provides a large coefficient of friction. The, large frictional resistance is produced between the end surface of each tapered roller and the surface of the cone back face rib. This also increased the torque and the amount of heat produced initially. Especially, if the tapered rollers are spaced a large distance from the inner and outer rings to form a thick film of lubricating oil, thereby increasing the viscous resistance as described above, the tapered rollers are skewed by the viscous resistance. At this time, the surface of the cone back face rib drags the large end faces of the tapered rollers, producing larger frictional resistance.